The relative potency and interrelationship among vasoactive and natriuretic factors are thought to be important in the transition from fetal to neonatal life. However, little is known about their potential roles in the perinatal setting. Recently, we have reported umbilical cord levels of these factors in vaginally delivered newborns and evaluated their possible functions. Based on the published literature as well as our reports, I will summarize current knowledge about the clinical and biological roles of these mediators, i.e., vasopressin (AVP), endothelin-1 (ET-1), adrenomedullin (AM), uroguanylin, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and nitric oxide (NO), in the transition from fetus to neonate. Successful transition from in utero environment to air breathing may be associated with initially high levels of AVP, ET-1, AM and uroguanylin with apparently normal ANP, BNP and NO, and with a close relationship between ET-1 and AM. As blood levels of AVP and ET-1 decrease postnatally, the levels of ANP, BNP and NO increase. These characteristic changes and interrelationships of the factors may be adaptationally related to the circulatory and renal transition from fetal to neonatal life. It is also suggested that an imbalance among these factors may be linked to the transition failure states, e.g., birth asphyxia, circulatory shock, persistent pulmonary hypertension of the newborn, sepsis and renal failure.
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